The study aims to investigate the differences in the mechanism of growth cone migration to a positive guideline cue by examination of growth cone turning and branching toward a point of neurotrophic factors (NGF,BDNF, NT-3) in neunatal, adult and old rats. We will record the behaviour of growth cones as well as their approach to neurotrophic factors. After fixing and labeling them, we shall localize the microtubules and act in filaments and analize their videomicroscopic images. We will apply drugs to determine the role of neurotrophic factors in the mechanisms of this response and identify the sensitivity of involving receptors. We will investigates some steps of signal transduction events, that mediates the turning and branching toward a point source of NGF (the influx of Ca++, activation of trk signaling cascade, autophosphorialation of trkA and PI-kinase), as well as their differences in the experimental groups. The results of these experiments would clarify the difference between the regenerative capacity of neurons from neonatal, adult and aged rats and the processes of cell regeneration at molecular level. It will clarify the fine processes of the nervous tissue regeneration and the abilities of the peripheral neurons to regenerate and repair axonal pathways that are injured or damaged by different disease.